1. Field of the Invention
The present invention is generally in the field of electrical circuits. More specifically, the invention is in the field of voltage controlled oscillators.
2. Related Art
In the field of wireless communication, such as radio frequency (“RF”) communication, voice and data signals are encoded over a carrier signal prior to transmission. Typically, the carrier signal used for RF communication is a sine wave generated by an oscillator. For example, a typical oscillator used to generate a sine wave for RF communication is a voltage controlled oscillator (“VCO”).
A conventional VCO generally includes a tank circuit for establishing the oscillation frequency of the output signal generated by the VCO. When the VCO and the tank circuit are integrated into a semiconductor device, the oscillator is also referred to as an “on-chip” VCO using an “on-chip” tank circuit. In operation, the capacitive value of the tank circuit is adjusted in order to tune the output of the VCO to a desired oscillation frequency. Furthermore, in order to accommodate process variations associated with inductive and capacitive components of an on-chip VCO employing an on-chip tank circuit, conventional on-chip VCOs typically employ coarse tuning and fine tuning to vary the capacitive component of the on-chip tank circuit.
Current implementations of coarse tuning, however, have a number of significant drawbacks. In particular, conventional coarse tuning techniques typically require special synthesizer programming. For example, specialized look-up tables and look-up routines may be required to support conventional coarse tuning. In other cases, significant synthesizer hardware modification. Accordingly, there is a strong need in the art for an efficient circuit and method for tuning an on-chip VCO, which does not require specialized synthesizer programming or synthesizer hardware modification.